As ultrawide bandwidth (UWB) technology becomes increasingly desirable for wireless devices, it becomes more and more necessary to set a standard for UWB operations. The Institute for Electrical and Electronic Engineers (IEEE) has designated that the 802.15.3™ standard be drafted to cover high rate wireless personal area networks (WPANs), which covers UWB communications. This standard will ultimately define both a UWB medium access control (MAC) layer and a UWB physical (PHY) layer.
At present, two proposed standards for the physical (PHY) layer for this standard are under consideration by the IEEE under the designation 802.15.3a™. The first is a direct sequence ultrawide bandwidth (DS-UWB) proposal; the second is a multiband orthogonal frequency division multiplexing (MB-OFDM) proposal.
MB-OFDM is a UWB PHY layer protocol that uses a combination of frequency hopping and orthogonal frequency division multiplexing (OFDM) to wirelessly send data between devices at up to 480 Mbps.
The MB-OFDM approach divides the available spectrum into several different UWB bands. Information is then transmitted using OFDM modulation in each of these bands. The OFDM carriers are generated using a 128-point IFFT/FFT with a constellation limited to quadrature phase shift keying (QPSK). Information bits are then interleaved across all of the bands that are used.
The proposed MB-OFDM UWB system uses 528 MHz bands and provides a wireless personal area network (PAN) with data payload communication capabilities of 55 Mbps, 80 Mbps, 110 Mbps, 160 Mbps, 200 Mbps, 320 Mbps, and 480 Mbps.
This MB-OFDM system uses a total of 122 sub-carriers that are modulated using QPSK. Forward error correction coding (convolutional coding) is used with a set coding rate. The proposed MB-OFDM UWB system also supports multiple modes of operations: a mandatory 3-band mode (called Mode 1), and an optional 7-band mode (called Mode 2).
In the 3-band mode, the MB-OFDM system operates by transmitting successive OFDM symbols in different “sub-bands” using a frequency hopping technique. The proposed MB-OFDM UWB system uses three specific bands that are defined for use between 3.1 and 4.8 GHz.
In addition, four other bands are defined between 6.0 and roughly 8 GHz for systems for use in the optional 7-band frequency-hopping mode
Direct sequence ultra-wideband (DS-UWB) is a second UWB PHY layer protocol that uses high rate, ultra-wide bandwidth pulses to send data at rates up to 1000 Mbps. One particular DS-UWB approach divides the available spectrum into upper and lower bands, the lower band being between 3.1 to 5.15 GHz and the upper band being between 5.825 and 10.6 GHz. Information is then encoded using direct-sequence spread spectrum techniques. In particular, pulse filtering/shaping used with BPSK/QPSK modulation with 50% excess bandwidth, root-raised-cosine impulse response. The chip rate, center frequency and symbol rate are harmonically related, and a reference frequency of 684 MHz is used.
Because it is possible that devices using the MB-OFDM approach and the DS-UWB approach will both reach the market at the same time, it is desirable to provide a way in which MB-OFDM devices and DS-UWB devices could coexist within a single network.
However, these two UWB formats are fundamentally different from each other, and signals sent using one of these formats would be unreadable by devices designed to use the other format. Furthermore, should additional formats be introduced, it's likely that those new formats would also be incompatible with existing formats.
Accordingly, it would be desirable in the art for a solution to the problems associated with using multiple formats for different wireless devices. In particular, it would be desirable to allow devices to have at least minimal communications with each other, regardless of their primary communications format.